Japanese Laid-open Patent Publication No. 2010-077960 discloses a technique for controlling an electronic throttle valve by selecting, when a driver demand drive force (i.e., a drive force demanded by the driver and calculated based on an accelerator opening degree) is greater than a target drive force for limiting vehicle speed, the smaller of these two, that is to say, the target drive force for limiting vehicle speed, so that actual vehicle speed does not exceed a limit vehicle speed.
Here, a configuration is assumed in which an acceleration for limiting vehicle speed (referred to as “vehicle speed limit acceleration”, hereinafter) is calculated based on a difference between actual vehicle speed and limit vehicle speed, a target drive force for limiting vehicle speed (referred to as “vehicle speed limit drive force”, hereinafter) is calculated based on the vehicle speed limit acceleration, a driver demand drive force is calculated based on an accelerator opening degree, and a drive force is controlled based on the smaller of the vehicle speed limit drive force and the driver demand drive force. In other words, when the driver demand drive force is greater than the vehicle speed limit drive force, the drive force is limited to the vehicle speed limit drive force.
Here, a state in which the vehicle speed limit drive force is smaller than the driver demand drive force and thus the drive force is controlled based on the vehicle speed limit drive force is referred to as “a limit state”, and a state in which the vehicle speed limit drive force is greater than the driver demand drive force and thus the drive force is controlled based on the driver demand drive force is referred to as “a non-limit state”.
The vehicle speed limit drive force is calculated based on the vehicle speed limit acceleration; however, in order to reduce a probability that the actual vehicle speed exceeds the limit vehicle speed, it is necessary to correct the vehicle speed limit drive force based on a traveling circumstance. Because the drive force is controlled based on the vehicle speed limit drive force in the limit state, the vehicle speed limit drive force can be corrected based on a difference between an actual acceleration and the vehicle speed limit acceleration. However, because the drive force is controlled based on the driver demand drive force in the non-limit state, the vehicle speed limit drive force cannot be corrected based on a difference between an actual acceleration and the vehicle speed limit acceleration. This is because in the non-limit state the actual acceleration is not an acceleration that is achieved as a result of controlling the drive force based on the vehicle speed limit acceleration but instead is an acceleration that is achieved as a result of controlling the drive force based on the driver demand drive force.
For this reason, in the non-limit state the vehicle speed limit drive force cannot be corrected based on the traveling circumstance. If the vehicle speed limit drive force is corrected based on the traveling circumstance in the non-limit state, the vehicle speed limit drive force may exceed an appropriate value under a certain traveling circumstance, which may cause the actual vehicle speed to exceed the limit vehicle speed. Further, the vehicle speed limit drive force may fall below an appropriate value under another circumstance, which may cause the drive force to be excessively limited, which in turn causes the driver to feel strange.
Therefore, it is an object of one aspect of the disclosure to provide a vehicle speed limit apparatus that calculates an upper limit value in a non-limit state based on a current drive force generated by a drive force generation apparatus, thereby increasing smoothness of a transition from the non-limit state in which a demand value is selected to a limit state in which the upper limit value is selected.